The synthesis of complex cyclic natural products has provided an impetus for the development of new and efficient methods for the annulation of rings. During the past two years we have demonstrated that the intramolecular addition of allylsilanes to electrophilic olefins is capable of producing a remarkably large number of bicyclic ring systems. To date we have utilized these findings in stereospecific syntheses of the sesquiterpenes nootkatone, widdrol, and perforenone-A. In this proposal we apply our method for ring formation to several of the naturally occurring polyquinanes which of late have attracted considerable attention because of their novel structures and biological activities. The object of this proposal is not simply to present "new" approaches to these "old" molecules using known chemistry; but rather to highlight the versatility and advantages unique to our carbocyclization procedures. Our unified approach to the linear-triquinanes hirsutene and capnellene exploits the capability for diastereoselection in the cyclization of allylsilanes. We also propose a novel bis-annulation process and intend to use it for the construction of a common precursor which permits the efficient synthesis of several fused-triquinanes and the biologically important sesquiterpenes pentalenolactone E and G; our use of a common precursor contrasts with other known strategies.